Migrations scramble history. Without a dated baseline, every later comparison becomes a negotiation. A Metrics Baseline Workshop exists to freeze a small set of application KPIs while the old world still runs.
Freeze collection windows
Agree the exact calendar window — often the last six weeks of stable operation. Document exclusions such as known outage weekends so nobody “corrects” the baseline later in secret.
Prefer owners over spectators
Invite people who will collect the post-migration numbers. Sponsors may observe; the baseline sheet needs signatures from application owners and the operations lead who will live with the definitions.
Resist inventing new KPIs mid-workshop
Baselines are for continuity. New measures belong in a separate framework design engagement. Mixing the two produces a sheet nobody trusts.
Leave with a dated baseline, named owners, and a plan for the first comparison after cutover. That package is modest — and it prevents months of contested storytelling.